Richard Castle: [looking at a dead woman with a misspelled message on her face] Whoever killed her also murdered the English language.
Det. Roselyn Karpowski: Beckett, you are never gonna believe this
Kate Beckett: Oh, the bar on unbelievable is pretty high right now.
Richard Castle: It's a common mistake, but it's not ironic that Dr. Cosway's not here for you to lean on. It's just simply tragic. It would be ironic if her death made you feel better.
Lanie Parish: Quit looking at the girls, Castle.
Richard Castle: Roger that.
[Kate, Esposito, and Ryan are stuck on their respective cases]
Kate Beckett: We've been over these cases so many times, it's hard to see straight anymore. All right. We'll start over. Fresh eyes. You take our murder, we'll take yours.
Javier Esposito: All right.
Richard Castle: Whoa, whoa, whoa, whoa. Say that again.
Kate Beckett: You take our murder, we'll take yours.
Richard Castle: Could it be that easy? You take mine, I'll take yours.
Javier Esposito: What are you getting at, Castle?
Richard Castle: "Strangers on a Train".
Kevin Ryan: The Hitchcock movie?
Richard Castle: I'm partial to the novel by Patricia Highsmith, but yes. We have two strong suspects, but with airtight alibis, right?
[Castle takes pictures of suspects off the murder board]
Javier Esposito: Right.
Richard Castle: We know they're connected. What if the connection is the killers?
Kate Beckett: Jason and Eric committed each other's murders.
Richard Castle: And made sure they had an airtight alibi for the murder they knew they'd be suspected of. It's not our victims who are connected. It's our murderers. Crisscross!